This invention pertains to diagnostic tools used to diagnose faults in automotive vehicle wiring, and more particularly, to a bus isolation/diagnostic tool used to isolate the bus signals from modules connected to a common bus in a control module by common connectors.
Automotive vehicles are increasingly using a wide variety of electronic devices. In many cases, these electronic devices communicate with a central control unit, such as a body controller or engine controller. One increasingly common technique of providing the communication link between electronic devices and the central control unit is the use of a common bus, such as the Society of Society of Automotive Engineers (SAE) J1850 Surface Vehicle Standard entitled Class B Data Communications Network Interface, Revised May, 1994, ("J1850 Bus").
In one implementation using the J1850 Bus, such as the one used in certain motor vehicles manufactured by Chrysler Corporation, various electronic modules are connected to a body controller and communicate with the body controller over a common J1850 Bus. All modules on the J1850 Bus are linked together at a common node internal to the body controller and a separate wire connects each module to the J1850 Bus. These separate wires, along with other wire from the modules, are part of the wiring harness of the motor vehicle and are connected to the body controller using one more common connectors. That is, each wire is connected to a separate pin or terminal in the connector or connectors that attach to a corresponding body controller connector or connectors. In turn, the body controller's connector or connectors have pins that are connected to appropriate inputs and outputs of the body controller's connector. The pins to which the J1850 wires of the various electronic modules are connected all connect to the common J1850 bus on the body controller.
The disadvantage that the foregoing arrangement has is that the J1850 connection for the individual electronic modules cannot be individually connected to and disconnected from the body controller at the body controller. Rather, any such individual connections and disconnections must be done at each electronic module. This presents a problem in diagnosing faults in the J1850 communication circuits in the individual electronic modules. Since the J1850 bus is a common bus, if the J1850 circuit of an electronic module fails in a manner that its output is always high (such as shorted to voltage) or low (such as shorted to ground) the J1850 bus will be forced high or low. Therefore, to diagnose such a fault in an individual module, it is often necessary to disconnect and reconnect the electronic modules from the J1850 bus to isolate and identify the electronic module having the fault. This proves to be a cumbersome process as the disconnections and connections must be made at each of the individual electronic modules rather than at the body controller due to the fact that the wiring harness has a common connector or connectors at which all the J1850 circuits terminate. Moreover, connections from the electronic modules to the body controller must often be maintained during the diagnostic process.
It is an object of this invention of alleviating the foregoing cumbersome by providing a bus isolation/diagnostic tool that allows electronic modules to be selectively connected to the common bus in the central controller and that allows connections to the central controller made by the common connector(s) to be maintained.
It is also an object of this invention to provide a bus isolation/diagnostic tool that determines whether a bus communication circuit in an electronic module fails high or low, or is within a specified range, and to accumulate high and low failures of the bus communication circuits of the electronic modules.